Movable barrier operators are well known in the art. Such operators typically respond to user commands (as provided through wired or wireless interfaces) to cause a corresponding movable barrier to move (usually such movement is back and forth between open and closed positions). Various movable barriers can be moved in such fashion, including vertically moving barriers (such as single-piece and segmented garage doors and rolling shutters of various kinds) and horizontally moving barriers (including both sliding and swinging gates and the like).
Such operators use a motive source, such as a motor, to cause such movement of a moving barrier. Sometimes, however, it is desirable to be able to move such a barrier without aid of the operator. For example, when emergency vehicles approach a gated community they need a method of entrance even if electricity is not available. It is known, for example, to provide a manual disconnect mechanism on a trolley that couples a garage door to a motor-driven chain to allow selective decoupling of the garage door from the garage door operator motor to thereby permit manual movement of the garage door. Such disconnect mechanisms, however, are typically accessible only from within the garage itself. Consequently, an otherwise authorized person located outside the garage may be unable to utilize such a disconnect mechanism and will therefore be unable to open the corresponding movable barrier by manual means. Similar problems occur with other varieties of movable barriers.
In one prior art approach, when electric power becomes unavailable, the corresponding movable barrier automatically becomes openable by manual means through use of a special non-gripping clutch. So configured, the drive mechanism will present little or no resistance to manual movement of the movable barrier. Although such an approach will allow opening of the barrier when power is absent, such an approach presents problems of its own. First, even unauthorized persons may now move the movable barrier when power is absent and hence gain access to the area beyond. Second, there may be times when manual entry is desired notwithstanding the availability of electric power; in such a case this prior art approach will not permit entry.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements (such as housings, drive chains, and movable barriers) that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.